This project will evaluate autologous marrow transplantation for patients with multiple myeloma. Initial studies will utilize a regimen of busulfan and cyclophosphamide with unpurged marrow to determine toxicity of the regimen, and repopulating ability of the marrow. In vitro studies will evaluate the efficacy of several different techniques for marrow purging including prednisone, monoclonal antibodies with complement and positive selection of hematopoietic precursor cells. Subsequent, clinical studies will evaluate engraftment using the most promising marrow purging technique. Future studies will explore different treatment regimens and transplantation earlier in the disease course with the ultimate goal of developing curative strategies.